This invention relates to a technique for locating a non-conductive casing, such as a concrete or clay sewer pipe, as the casing is pushed through the earth during installation.
Utilities, such as those providing electric, gas, water, and/or telephone service, often bury their conveyances (i.e., pipes and/or cables) underground for reasons of safety and aesthetics. In urban environments, excavation often occurs in close proximity to such buried conveyances. In the past, excavation occurring in close proximity with buried fiber optic communications cables has led to cable cuts that result in extensive service outage. A greater risk occurs when excavating in close proximity to buried pipelines carrying natural gas or gasoline. Inadvertent damage to such buried pipelines can lead to fire and/or explosion,
Techniques currently exist for locating buried underground conveyances by impressing a radio frequency locating signal on the conveyance and then monitoring the locating signal radiated above the ground by the conveyance as taught in U.S. Pat. No. 5,644,237, issued in the names of Hossein Eslambolchi and John Huffman, on Jul. 1, 1997, and assigned to ATandT. Now-allowed U.S. patent application Ser. No. 09/503,384, filed in the names of Hossein Eslambolchi and John Huffman, on Jul. 1, 1997, and assigned to ATandT, describes a technique for monitoring a boring head performing a boring operation underground in proximity to one or more buried utility conveyances. The technique described in the aforementioned ""384 application relies on monitoring a radio frequency signal radiated above the ground from the boring head to determine the location of the boring head relative to nearby underground conveyances.
A problem related to monitoring the boring head during a boring operation is the problem of monitoring the location of a large water or sewer pipe during installation underground. Often, because of the inability to excavate an open trench, a contractor will install such large pipes, hereinafter referred as xe2x80x9ccasings,xe2x80x9d by pushing the casing through the earth, much like pushing a boring head during a boring operation. Unfortunately, the boring head monitoring technique described in the now-allowed ""384 application cannot be readily employed to monitor the installation of casings made from clay or concrete since neither material can carry a locating signal in contrast to the metallic bore head. Consequently, there currently exist no other techniques for monitoring the location of a concrete or clay casing during installation. This often poses a problem because the forward of the casing may wander off the casing centerline by as much as 10% of the casing length when the forward end is pushed through the earth. Thus, for example, the forward end of a 50 foot long casing can wander as much as five feet off the casing centerline during installation.
Thus, a need exists for a technique for monitoring the position of a non-conductive casing, such as a water or sewer pipe made from concrete or clay, during installation.
Briefly, in accordance with a preferred embodiment, there is provided a technique for monitoring the location of a non-electrically conductive casing as it is pushed through the earth. In accordance with the method, a water pipe is attached to the casing to run the length thereof. The pipe member has a closed first end and a second end attached to a reservoir of water or another electrically conductive liquid whose level varies in accordance with the horizontal orientation of the casing. A locating signal transmitter transmits a radio frequency locating signal into the water carried by the pipe so that the water radiates the locating signal above the ground. Using a signal-monitoring device to detect the locating signal radiated above the ground, a contractor can monitor of the location of the casing during installation.